Angiographic and guide catheters are well known in the field of medicine for use in conjunction with other catheters for the treatment of cardiovascular disease through such procedures as percutaneous transluminal coronary angioplasty (PTCA) procedures. Guide catheters aid in treatment of arterial lesions by providing a conduit for positioning dilatation balloon systems across an arterial stenosis. Angiographic catheters aid in delivering radiopaque dyes and the like into selected blood vessels to allow angiographic examination and the like of the blood vessels. The need for a greater variety of catheters to treat different types of circumstances has grown tremendously as the techniques for the use of such devices has grown.
During the treatment of cardiovascular disease, guide catheters and diagnostic catheters must be able to traverse tortuous pathways through blood vessels in a manner that minimizes trauma. In order for the physician to place the catheter at the correct location in the vessel, the physician must apply longitudinal and rotational forces thereto. Catheters must typically be stiff enough to transmit the required forces, while at the same time flexible enough to maneuver through the vascular system. For optimum performance and control, a catheter must achieve a balance between these often competing factors.
In many applications the catheter is guided through the aorta, over the aortic arch, and down to the ostium of the vessel which is to be treated or diagnosed. To reach such sites, the proximal section of the catheter is typically relatively rigid for transmitting the forces applied, and the distal section is more flexible to allow for better tracking and placement of the catheter within the vessels. One approach to increase the strength of the proximal section is to include a metal braid or coil therein. Another approach is to merely use a stiffer polymer in the proximal portion than in the distal portion.
In many surgical procedures, it is important to determine the location or position of the catheter within the body. This is often accomplished by incorporating a radiopaque material in the catheter. X-ray observation techniques can then be used to view the position of the catheter within the body.
It is known to mix a radiopaque material, typically in a powder or granular form with the plastic material of the catheter. One potential limitation of this approach is that the inner and outer surfaces of the catheter may become rough or course. This may be particularly problematic when the concentration of the radiopaque filler material is high, especially near the surface. For some radiopaque filler materials, high concentrations may be required to achieve the desired X-ray visibility. Another limitation may be that the radiopaque filler material may cause the plastic binder materials to lose their original and desired thermoplastic properties. Hard granular radiopaque materials in particular may detract from the desired flexibility ductility and maneuverability of the resulting tubing in direct proportion to the amount of radiopacity that they impart.
One approach for overcoming some of these limitations is disclosed in U.S. Pat. No. 4,657,024 of Coneys. Coneys suggests completely embedding and surrounding a radiopaque layer with a non-radiopaque plastic material. Presumably, since the plastic material that surrounds the radiopaque layer does not include any radiopaque filler materials the inner and outer surfaces of the medical-surgical tube can be made smooth.
Another approach is disclosed in U.S. Pat. No. 3,618,614 of Flynn. Flynn suggests providing one layer that is transparent to X-rays adjacent to another layer that is radiopaque. Flynn also suggests adding at least one material having plasticising properties or, in the alternative, providing a polymeric material which imparts greater flexibility and softness to the plastic material of the radiopaque layer so that the plastic material of the blend retains its desired properties of plasticity, softness and flexibility.
In both Coneys and Flynn, at least one layer is free from radiopaque filler material. Since it is often desirable to minimize the wall thickness of many catheters and maximize the radiopacity thereof, it would be beneficial to provide a multi-layer catheter tubing that includes at least some radiopaque material in at least two of the layers thereof. This may increase the X-ray visibility of the resulting catheter within the body.